Filler comprising fly ash for use in polymer composites

ABSTRACT

The present invention is a fly ash filler or filler blend having a particle size distribution with at least three modes that can be combined with a polymer at higher filler loadings to produce a filled polymer for polymer composites that, in many cases, can produce improved mechanical properties for the polymer composites over polymer composites using conventional fillers. As a result, superior polymer composites (e.g. those used in carpet backing) can be produced at a lower cost than conventional polymer composites. The present invention also includes a method for producing a polymer composite, comprising the steps of combining a polymer with a fly ash filler or a filler blend having a particle size distribution with at least three modes to produce a filled polymer and producing a polymer composite with the resulting filled polymer. The present invention further includes a method of determining what fly ashes can be used as fillers for polymer composites.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/068,126, filed Feb. 28, 2005, now U.S. Pat. No. 7,241,818 which is acontinuation of U.S. patent application Ser. No. 10/225,958, filed Aug.22, 2002, now U.S. Pat. No. 6,916,863 which is a continuation-in-part ofU.S. patent application Ser. No. 09/993,316, filed Nov. 14, 2001, nowU.S. Pat. No. 6,695,902 which claims the benefit of commonly owned, U.S.Provisional Application No. 60/248,518, filed Nov. 14, 2000, which ishereby incorporated herein in its entirety by reference

FIELD OF THE INVENTION

The present invention relates generally to fillers for polymercomposites such as those used for carpet backing, and more particularlyrelates to fly ash filler and filler blends for use in polymercomposites and to methods for selecting or modifying a fly ash filler orfiller blend for use in polymer composites.

BACKGROUND OF THE INVENTION

Polymers are used in various types of applications and often utilize amineral filler, or extender, both to impart desired mechanicalproperties and to reduce raw material costs. For example, the mineralfillers typically used in polymers include calcium carbonate, kaolin,talc, mica, wollastonite, silica, glass flakes and glass spheres.

Recently, there has been an increased interest in using fly ash as afiller in polymer composites. In particular, because fly ash is arecycled material produced by the combustion of coal, fly ash qualifiesas a recycled material and thus is desirable for this reason. Fly ash isalso relatively inexpensive when compared to the fillers often used asfillers for polymer composites. Furthermore, it has been discovered thatfly ash can be used in polymer composites without causing detriment tothe mechanical properties of the polymer composites and, in many cases,improving the mechanical properties of the polymer composites.

Numerous references describe the use of fly ash in polymer composites.For example, U.S. Pat. No. 6,091,401 to Jenkines describes the use ofClass F fly ash fillers in polyurethane carpet backing. Although thesereferences describe polymer systems that can use fly ash, there is aneed in the art to increase the filler loadings in polymer composites todecrease the cost of producing the polymer composites and, in manycases, to further improve the mechanical properties of the polymercomposites.

SUMMARY OF THE INVENTION

The present invention provides a filler comprising fly ash that can beused in polymer composites and methods of classifying fly ash orblending a fly ash with at least one additional filler such as anadditional fly ash to produce a filler for polymer composites. Inparticular, the filler comprising fly ash has a particle sizedistribution having at least three modes and can often be used at higherloadings than have previously been possible for the particular polymercomposite. As shown in related U.S. application Ser. No. 09/993,316,filed Nov. 14, 2001, which is incorporated by reference herein in itsentirety, the fly ash fillers of the invention can be used at higherloadings to produce greater mechanical properties in asphalt shingles,which are one type of polymer composite in accordance with theinvention.

The inventors have discovered that the granulometry of the fly ash usedas a filler or in filler blends for polymer composites is important tothe Theological performance of the filled polymer in the production ofthe polymer composites and to the mechanical properties of the resultingpolymer composites. In one embodiment of the invention, the polymercomposite includes filled polymer comprising a polymer and a filler, thefiller comprising fly ash and having a particle size distribution havingat least three modes and typically having three modes. Preferably, theparticle size distribution includes a first mode having a medianparticle diameter from 0.3 to 1.0 microns, a second mode having a medianparticle diameter from 10 to 25 microns, and a third mode having amedian particle diameter from 40 to 80 microns. The particle sizedistribution also preferably includes 11-17% of the particles by volumein the first mode, 56-74% of the particles by volume in the second mode,and 12-31% of the particles by volume in the third mode. Moreover, theratio of the volume of particles in the second and third modes to thevolume of particles in the first mode is preferably from about 4.5 toabout 7.5. In one embodiment, the filler consists of a fly ash having aparticle size distribution having at least three modes and the filledpolymer includes at least one additional filler other than the fly ash.In other words, the filled polymer includes at least one additionalfiller that may not be selected to produce a filler having the particlesize distribution described above. The filled polymer can be used toproduce various types of polymer composites including carpet backing.

In one preferred embodiment, the filler used in the filled polymer forthe polymer composite comprises a blend of fly ash and at least oneadditional filler wherein the filler blend has a particle sizedistribution having at least three modes and typically having threemodes. The fly ash can, for example, be a lignite coal fly ash or asubbituminous coal fly ash. Moreover, the fly ash filler can be a ClassC or Class F fly ash filler. In one preferred embodiment, the at leastone additional filler in the filler blend is a second fly ash. For thisembodiment, the filler blend preferably comprises a high fine particlecontent fly ash filler (e.g. having a median particle size of 10 micronsor less) and a low fine particle content fly ash filler (e.g. having amedian particle size of 20 microns or greater). Alternatively, the atleast one additional filler in the filler blend can be another mineralfiller such as calcium carbonate. In this particular embodiment, the flyash is preferably a high fine particle content fly ash. The filler blendcan include from about 10% to about 90% by weight of the fly ash fillerand from about 90% to about 10% by weight of the additional filler. Inone embodiment, the filler blend comprises a first fly ash and at leastone additional filler selected from the group consisting of a second flyash and calcium carbonate, and the polymer composite comprises at leastone additional filler other than the fillers included in the fillerblend. In other words, the filled polymer includes at least oneadditional filler that may not be selected to produce a filler blendhaving the particle size distribution described above.

The filler blend preferably has a packing factor of at least 65% and canbe loaded in the filled polymer at a filler loading of greater than 20%to about 80% percent by weight, preferably from about 30% to about 80%by weight, and more preferably from about 40% to about 80% by weight.The filler can also be loaded in the filled polymer at a filler loadingof greater than 20% to about 60% percent by volume, preferably fromabout 30% to about 60% by volume, and more preferably from about 40% toabout 60% by volume. Although various polymers can be used in thecomposite as discussed herein, the polymer is typically selected fromthe group consisting of polyethylene, polypropylene, polyvinyl chloride,nylons, epoxies, phenolics, polyesters, acrylic polymers, polyurethanes,bitumen, styrene-butadiene copolymers, acrylonitrile-butadiene-styrenecopolymers and blends thereof. The polymer composites can be used innumerous applications such as in carpet backing and can be loaded inamounts, e.g., greater than 55% by weight. The present invention furtherincludes a filler for filled polymers for polymer composites comprisinga blend of fly ash and at least one additional filler and having aparticle size distribution with at least three modes as discussed above.

The present invention also includes a method for producing a polymercomposite, comprising combining a polymer with a filler to produce afilled polymer, the filler comprising fly ash and having a particle sizedistribution with at least three modes; and producing a polymercomposite with the resulting filled polymer. The filler preferably has aparticle size distribution having the properties discussed above. Thefiller can be produced in accordance with the invention by classifying afly ash to produce a fly ash filler having a particle size distributionhaving at least three modes. The fly ash filler can then be combinedwith the polymer and at least one additional filler to produce thefilled polymer. Alternatively, the filler can produced by blending flyash and at least one additional filler and the filler blend combinedwith the polymer to produce the polymer composite. For example, thefiller blend can be produced by blending a first fly ash and a secondfly ash or by blending a fly ash and at least one additional fillerother than fly ash (e.g. calcium carbonate). The filler for use in thepolymer composite can also be produced by burning two or more types ofcoal selected from the group consisting of lignite coal, subbituminouscoal and bituminous coal. In one embodiment, the filled polymer can beused to produce carpet backing.

In one particularly preferred embodiment, the present invention includescarpet backing formed of a filled polymer comprising a polymer selectedfrom the group consisting of polyethylene, polypropylene, bitumen,styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymerand blends thereof, and filler, the filler comprising fly ash and havinga particle size distribution having at least three modes. A carpetmaterial in accordance with this embodiment can be produced by combininga polymer selected from the group consisting of polyethylene,polypropylene, bitumen, styrene-butadiene copolymer,acrylonitrile-butadiene-styrene copolymer and blends thereof, with afiller to produce a filled polymer, the filler comprising fly ash andhaving a particle size distribution with at least three modes, andapplying the filled polymer as a melt to a surface of a carpet materialat an elevated temperature to form a backing on the carpet material. Forexample, the filler can be used in the filled polymer at a fillerloading of greater than 55% by weight. The filled polymer can be formedinto filled polymer pellets and these pellets subjected to an elevatedtemperature to produce a filled polymer melt that can be applied to thesurface of the carpet material. The method can include the step ofremoving at least the fly ash particles having a particle size ofgreater than 250 microns prior to combining the filler with the polymer.For example, the fly ash particles having a particle size of greaterthan 250 microns can be removed by using (i.e. passing the fly ashthrough) at least one screen having a mesh size between about 75 andabout 250 microns to remove at least said fly ash particles having aparticle size of greater than 250 microns. Alternatively, the fly ashparticles can be air classified to remove at least said fly ashparticles having a particle size of greater than 250 microns.

In yet another embodiment of the invention, the present inventioncomprises a method for producing a polymer composite, comprising thestep of selecting a fly ash filler for use in the polymer composite ormodifying a fly ash filler for use in the polymer composite to have aparticle size distribution with at least three modes to increase thepacking factor of the fly ash filler and to improve the mechanicalproperties of the polymer composite. Typically, the fly ash filler willhave three modes. The polymer can also be selected to have goodcompatibility with the fly ash filler to improve the mechanicalproperties of the polymer composite.

These and other features and advantages of the present invention willbecome more readily apparent to those skilled in the art uponconsideration of the following detailed description, which describe boththe preferred and alternative embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, preferred embodiments aredescribed in detail to enable practice of the invention. Although theinvention is described with reference to these specific preferredembodiments, it will be understood that the invention is not limited tothese preferred embodiments. But to the contrary, the invention includesnumerous alternatives, modifications and equivalents as will becomeapparent from consideration of the following detailed description.

As discussed above, the inventors have determined that the granulometryof fly ash fillers and filler blends is the dominant factor indetermining the suitability of these fillers for use as mineral fillersin polymer composites. As is well understood to those skilled in theart, fly ash is produced from the combustion of pulverized coal inelectrical power generation plants. Fly ash is formed of mineral matterthat is typically of very fine particle size, ranging from less than 1micron to over 100 microns in some cases. The fly ash particles possessa substantially spherical shape as a consequence of the high temperaturemelting and coalescence in the furnace of the mineral matteraccompanying the coal. The fine particle size and spherical shape areadvantageous properties of the fly ash and are in marked contrast to theproperties of many conventional fillers such as ground limestone orcalcium carbonate, which are typically relatively coarse with anirregular, blocky particle shape. These differences in granulometrybetween fly ash and these conventional fillers are highly significant tothe present invention.

Mineralogically, fly ash is predominantly amorphous, or non-crystalline,in nature as a result of the rapid quenching of clay/shale minerals asthey rapidly pass through the boiler flame and dust collection system ofthe power plant. For some fly ashes, the amorphous material can bedescribed as an aluminosilicate glass similar in composition to themineral mullite (Al₆Si₂O₁₃); for other fly ashes, it can be described asa calcium aluminosilicate glass similar in composition to the mineralanorthite (CaAl₂Si₂O₈). Fly ashes also contain smaller amounts of avariety of other mineral components derived from thermal modification ofaccessory minerals present in the coal. These typically include mullite,quartz (SiO₂), ferrite spinel (Fe₃O₄), hematite (Fe₂O₃), dicalciumsilicate (Ca₂SiO₄), tricalcium aluminate (Ca₃Al₂O₆), and lime (CaO).These mineral components occur either as inclusions in the glassparticles or as discrete particles.

It is commonly known that the chemical composition of fly ash changes asa result of the type of coal being burned in the boiler. Thesedifferences are largely in the relative proportions of the elementcalcium present in the ash. For example, high rank bituminous coalsgenerally have a low calcium content and produce an ash with relativelylow calcium, typically less than 5% as CaO; whereas low rank thermalcoals generally have much higher content of calcium, typically in therange 8-20% CaO for lignite coals and 20-30% CaO, or higher, forsubbituminous coals. These differences are recognized by ASTMspecifications, such as ASTM C-618 that governs the use of fly ash as apozzolan in concrete in the United States and elsewhere, and by Canadianspecifications that classify the ashes based on their CaO content.

Current ASTM C-618 specifications include only two designations orclasses of fly ash: “Class F” and “Class C” fly ashes. The “Class F”designation generally incorporates fly ashes originating from thecombustion of bituminous and lignite coals and the “Class C” designationgenerally incorporates ashes from the combustion of subbituminous coals.These designations are based on the chemical composition of the fly ashin such a way that when the sum of the element oxides (SiO₂+Al₂O₃+Fe₂O₃)derived from chemical analysis of the ash is equal to or greater than70% by weight, then the fly ash is designated a “Class F” fly ash. Whenthe sum of the element oxides is equal to or greater than 50% by weight,the fly ash is designated as a “Class C” fly ash.

In Canada, as mentioned above, fly ashes have certain designations basedon their CaO content. In particular, a fly ash is considered a “Class F”when it includes less than 8% CaO, a “Class CI” when it includes 8-20%CaO, and a “Class CH” when it includes greater than 20% CaO.

It is less commonly known that the particle-specific properties, orgranulometry, of a fly ash also vary according to the source of the coaland the included mineral matter. In particular, this factor has a markedeffect on the proportions of the fine and coarse particles present inthe fly ash, also known as the particle size distribution, in concertwith the surface area and particle packing characteristics.Significantly, these properties are not addressed by appropriate ASTMspecifications, such as ASTM C-618, that cover the use of fly ash byindustry.

Thus, fly ash is a chemically, physically and mineralogically complexmaterial with properties that vary according to the source of the coalbeing burned in the power plant, as well as the combustion conditionsand pollution control equipment installed at the power plant. Anintimate knowledge of all these variables is essential to the successfuluse of fly ash as a mineral filler in polymeric products such as polymershingles. Furthermore, it is necessary that the filled polymer-fly ashcomposite meets applicable quality control specifications and ASTMperformance criteria.

The present invention discloses a methodology for selecting or modifyinga fly ash that will allow it to be used effectively as a substitute forthe conventional mineral fillers (e.g. calcium carbonate fillers) usedin polymer composites. The inherent properties of fly ash, or modifiedfly ash, allow a more economical polymer composite to be manufactured aswell as one with comparable or even superior mechanical properties andperformance.

In accordance with the invention, the inventors have discovered that thegranulometry of the fly ash is important in determining whether the flyash or a blend of the fly ash and another filler can be used to producepolymer composites and to improve the properties of polymer composites.In particular, a fly ash filler is selected for use in the polymercomposite having a particle size distribution with at least three modesto increase the packing factor of the fly ash filler and the mechanicalproperties of the polymer composite. Alternatively, the fly ash can beblended with another fly ash or with another filler to modify theproperties of the fly ash to produce a fly ash having a particle sizedistribution with at least three modes. Typically, the fly ash filler orfiller blend has a particle size distribution with three modes but canhave four, five or even more modes. In accordance with the invention, apolymer having good compatibility with the fly ash filler or fillerblends can be used to improve the mechanical properties of the polymercomposite. For example, as discussed in related U.S. application Ser.No. 09/993,316, filed Nov. 14, 2001, the fly ash fillers of theinvention can be used at higher loadings to produce greater mechanicalproperties in asphalt shingles, which are one type of polymer compositein accordance with the invention. For example, the fillers of theinvention have been found to increase the pliability, tear strength andtensile strength of asphalt composites. It is believed that the fly ashfillers of the invention can positively improve mechanical properties ofpolymer composites such as stiffness, strength, impact and temperatureresistance, dimensional stability, creep, surface hardness, scratchresistance, fire resistance and ultraviolet degradation. Moreover, a flyash filler or filler blend having a loss on ignition (or carbon content)within a certain desirable range can be selected for use with the filledpolymer to provide certain desired properties for the polymer composite.A fly ash filler or filler blend can also be used having a high specificgravity to provide certain properties to the polymer composite. Further,a fly ash filler or filler blend can also be used having a low oilabsorption to decrease the viscosity of the filled polymer inprocessing.

As mentioned above, it has been determined by the inventors that afiller comprising fly ash and having a particle size distribution withat least three modes has been found to be particularly advantageous foruse in filled polymers for use with polymer composites. Preferably, theparticle size distribution has three to five modes and typically hasthree modes. Preferably, the particle size distribution includes a firstmode having a median particle diameter from 0.3 to 1.0 microns, a secondmode having a median particle diameter from 10 to 25 microns, and athird mode having a median particle diameter from 40 to 80 microns. Insome cases, the filler can also include a coarse mode with a medianparticle diameter in the region of 100-200 microns and, in other cases,the filler can include an additional ultrafine mode with a medianparticle diameter in the region of 0.05-0.2 microns. The particle sizedistribution also preferably includes 11-17% of the particles by volumein the first mode, 56-74% of the particles by volume in the second mode,and 12-31% of the particles by volume in the third mode. Moreover, theratio of the volume of particles in the second and third modes to thevolume of particles in the first mode is preferably from about 4.5 toabout 7.5. It may also be desirable to remove coarse particles from thefiller, e.g., at least the particles having a particle size of greaterthan 250 microns. For example, as discussed in more detail below, atleast the coarse particles having a particle size of 50 microns can beremoved by various methods (e.g. screening or air classification) aslong as the filler maintains a particle size distribution having atleast three modes.

The filler preferably has a packing factor of at least 65%, andtypically has packing factors in the range of 65% to 75% and moretypically in the range of 67% to 73%. The filler of the invention canadvantageously be used at filler loadings of greater than 20% to about80% percent by weight, preferably from about 30% to about 80% by weight,and more preferably from about 40% to about 80% by weight. The fillercan also be loaded in the filled polymer at filler loadings of greaterthan 20% to about 60% percent by volume, preferably from about 30% toabout 60% by volume, and more preferably from about 40% to about 60% byvolume. As a result, the fillers of the invention can be used to replacesignificant amounts of polymer or other fillers in the polymer compositeand thus can greatly reduce the cost of the polymer composite.

The fly ash used in the filler according to the invention is a lignitefly ash, a subbituminous ash, a bituminous ash, or a blend of two ormore fly ashes (e.g. a subbituminous/bituminous blend). In addition, thefly ash can be a Class C fly ash, a Class F fly ash, or a blend thereof.More preferably, the filler is a lignite fly ash or a blend of a flyashes as discussed in more detail below. The fly ash filler typicallyhas a carbon content of from about 0.1% to about 15% by weight and canadvantageously be selected to have a carbon content of from about 1% toabout 5% by weight. It has been discovered that a carbon content greaterthan 5% can undesirably result in high viscosities when mixed with thepolymer. Although a filler having a carbon content less than 1% canadvantageously be used with the invention, a carbon content of 1% orgreater can, in some applications, result in a polymer composite havingimproved mechanical properties.

The filler of the invention can be a filler blend comprising a fly ashand at least one additional filler. In one embodiment of the invention,the filler blend can include a first fly ash and a second fly ash. Forexample, the filler blend can include a high fine particle content flyash filler such as a subbituminous coal fly ash (e.g. having a medianparticle size of 10 microns or less) and a low fine particle content flyash filler such as a bituminous coal fly ash (e.g. having a medianparticle size of 20 microns or greater). In addition, other blends offly ashes are possible such as bituminous/lignite, lignite/subbituminousand bituminous/lignite/subbituminous blends. In addition, two or morefly ashes from the same type of coal source, e.g., two different lignitecoal fly ashes, can be blended to produce the filler blend of theinvention. In the filler blends, the first fly ash can be included in anamount from about 0.1% to about 99.9%, more preferably from about 10% toabout 90% by weight of the filler blend and the second fly ash can beincluded in an amount from about 99.9% to about 0.1%, more preferablyfrom about 90% to about 10% by weight of the filler blend. The fillerblend typically has a carbon content of from about 0.1% to about 15% byweight and can advantageously be selected to have a carbon content offrom about 1% to about 5% by weight as discussed above. Although the flyash filler blend can be produced by blending two different fly ashes,the fly ash filler blend can also be formed by burning at least twodifferent coals selected from the group consisting of bituminous coals,lignite coals and subbituminous coals, and using the resulting ash asthe filler blend. For example, a subbituminous coal and a bituminouscoal can be burned together to produce the filler blend.

In another embodiment of the invention, the filler can be a filler blendincluding fly ash and at least one additional mineral filler other thana fly ash. Suitable mineral fillers include calcium carbonate, aluminumtrihydrate (ATH), milled glass, glass spheres, glass flakes, silica,silica fume, slate dust, amorphous carbon (e.g. carbon black), clays(e.g. kaolin), mica, talc, wollastonite, alumina, feldspar, bentonite,quartz, garnet, saponite, beidellite, calcium oxide, calcium hydroxide,antimony trioxide, barium sulfate, magnesium oxide, titanium dioxide,zinc carbonate, zinc oxide, nepheline syenite, perlite, diatomite,pyrophillite and the like, or blends thereof. In this embodiment, theadditional mineral filler is preferably calcium carbonate and thecalcium carbonate is preferably combined with a high fine particlecontent fly ash filler such as a lignite or subbituminous fly ash (e.g.having a median particle size of 10 microns or less). The filler blendcan include from about 0.1% to about 99.9%, more preferably about 10% toabout 90% by weight of the fly ash and from about 99.9% to about 0.1%,more preferably about 90% to about 10% by weight of the at least oneadditional filler. The fly ash can also be selected to produce a fillerblend having a carbon content of from 1% to 5% by weight as discussedabove or a primarily carbon-containing material (such as an amorphouscarbon) can be added to the filler blend, particularly in polymercomposites such as dark colored plastics where the presence of thecarbon-containing material is not undesirable. When additional fillersare blended with fly ash as the filler for the polymer composite, thefiller blend preferably has a particle size distribution with at leastthree modes as discussed above. Nevertheless, in some embodiments, thefly ash filler (and one or more additional fillers used in a fillerblend) will be selected to produce the particle size distributiondiscussed above and a further additional filler will not be selected forthis purpose.

In accordance with a preferred embodiment of the invention, the filleris a fly ash filler, a filler blend of two or more fly ashes, or afiller blend of fly ash and calcium carbonate, having the particle sizedistribution discussed above. In a more preferred embodiment, the fillerconsists essentially of a fly ash filler (either in the form of a singlefly ash filler or blend of fly ash fillers) having the particle sizedistribution discussed above.

The fillers used in the invention can be classified to produce a fillerhaving a particle size distribution with at least three modes asdiscussed above or one or more of the fillers used in the filler blendcan be classified to allow the filler blend containing the filler tohave a particle size distribution with at least three modes. Forexample, the fly ash fillers used alone or in the filler blends can beclassified to produce the desired particle size distribution. Forexample, a high fine particle content fly ash such as a subbituminouscoal ash or a high coarse particle content fly ash such as a bituminouscoal ash can be air classified to provide the desired particle sizedistribution. In addition to air classification, the fly ash fillers canbe classified using dry screening (sieving) or wet classificationmethods (e.g. wet screening or hydrocyclones) followed by drying of thefly ash. Alternatively, in-plant classification methods can be used. Forexample, the fly ash fillers can be classified electrostatically byadjusting the collection methods of the electrostatic precipitators usedto recover the fly ash from the electric power generation plants. Inaddition, the fly ash fillers can be classified by modifying thedischarge hopper selection of the fly ash from the electric powergeneration plants.

The polymer used in the polymer composites of the invention include notonly homopolymers but also copolymers of two or more monomers and theterm “polymer” as used herein includes plastics, resins, elastomers,thermoplastics, thermosets, and hot melts. Suitable polymers includespolyolefins (e.g. polyethylene or polypropylene), ethylene copolymers(e.g. ethylene-acrylic copolymers and ethylene-vinyl acetatecopolymers), polystyrene, polyvinyl chloride, polyvinylidene chloride,polyvinyl acetate, polyacrylonitrile, polyamides (e.g. nylon),polyisobutylene, acrylics, polyacetals, chlorinated and fluorinatedpolymers (e.g. PTFE), fluoroelastomers, fluorosilicones, polycarbonates,epoxies, phenolics, polyesters, acrylic polymers, acrylate polymers,polyurethanes, alkyds, silicones, bitumen (i.e. asphalt),styrene-butadiene (SB) latices, acrylonitrile-butadiene-styrene (ABS)latices, nitrile rubber, diallyl phthalates, melamines, polybutadienes,aramids, cellulosics, cellulose acetobutyrates, ionomers, parylenes,polyaryl ethers, polyaryl sulfones, polyarylene sulfides,polyethersulfones, polyallomers, polyimides, polyamide-imides,polymethylpentenes, polyphenylene oxides, polyphenylene sulfides,polysulfones, polyetherketones, polyethermides, polyaryleneketones,polychloroprenes, and blends thereof. Preferably, the polymer includespolyethylene, polypropylene, polyvinyl chloride, nylon, epoxies,phenolics, polyesters, acrylic polymers, polyurethanes, bitumen (i.e.asphalt), styrene butadiene copolymers, acrylonitrile-butadiene-styrenecopolymers, and blends thereof.

In addition to the polymer and the filler of the invention, the filledpolymer used in the polymer composites can include one or moreadditives. Suitable additives include surfactants, blowing agents, flameretardants, pigments, antistatic agents, reinforcing fibers (e.g. glassfibers), antioxidants, preservatives, water scavengers, acid scavengers,and the like. In addition, coupling agents can be used with the fly ashfillers of the invention for certain polymers. Suitable coupling agentsinclude silanes, titanates, zirconates and organic acids.

The polymer composites including the filled polymer of the invention canbe used in carpet backing, shingles and asphaltic products, automotiveproducts (e.g. sheet molding compounds, bulk molding compounds andinjection molded thermoplastic parts), commodity and engineeringplastics, pipe, conduit, polymer concrete, vinyl flooring, rubbermatting and other rubber products, paints, coatings, caulks, putties,dry-wall jointing compounds, adhesives, mastics and sealants. Thepolymer composite can include additional materials in combination withthe filled polymer as would be readily understood to those skilled inthe art.

The present invention also includes a method for producing a polymercomposite that includes the steps of combining a polymer with the fillerdiscussed herein to produce a filled polymer and producing a polymercomposite with the resulting filled polymer. Because the polymer isprocessed at an elevated temperature (e.g. 300-500° F.) to form a meltand to allow the polymer to have a workable viscosity, the filler can bepreheated prior to adding it to the polymer. Advantageously, by virtueof their lower specific heats, the fly ash fillers and fly ash fillerblends used in the invention can be preheated using less energy thanmany other fillers (e.g. calcium carbonate fillers) and thus can beprocessed at a lower cost. When the filler is a filler blend, each ofthe fillers can be added separately to the polymer but preferably thefiller blend is prepared prior to being added to the polymer so thefillers can be preheated together and so the desired particle sizedistribution can be produced. For example, the fly ash filler and atleast one additional filler can be blended together to form the fillerblend prior to preheating the filler blend and combining the fillerblend with the polymer. Alternatively, a fly ash blend can be formed byburning two or more types of coal selected from the group consisting oflignite coal, subbituminous coal and bituminous coal (e.g. by burning asubbituminous coal and a bituminous coal together) and used as thefiller blend for the polymer composite.

As mentioned above, the molten filled polymer preferably has asufficiently low viscosity to allow it to be processed to form thepolymer composite. The molten polymer can be processed at varioustemperatures known in the art and is preferably processed at atemperature between 200 and 500° F. Typically, the molten polymer has amelt viscosity of about 300-5000 centipoise or more (e.g. 400centipoise) at these processing temperatures. When the filler is addedto the polymer, the melt viscosity increases. Preferably, the filledpolymer has a melt viscosity below a particular threshold (e.g. about3000-10,000 centipoise) at the desired loadings so it can be effectivelyprocessed into the polymer composite. For example, the filler of theinvention can advantageously be used at filler loadings of greater thanabout 60% by weight, and even greater than about 70% by weight (e.g.even up to about 80% by weight) to produce the desired viscosity. Thefiller of the invention can also be used at filler loadings of greaterthan 40% by volume, greater than 50% by volume, and even up to about 60%by volume, to produce the desired viscosity. As a result, the fillers ofthe invention can be used to replace significant amounts of polymer inthe polymer composite and thus can greatly reduce the cost of thepolymer composite.

The molten filled polymer can be processed in any manner known in theart to produce the polymer composite. For example, suitable processingmethods include injection molding, extrusion, pultrusion, sheet moldingand the like.

In one particularly preferred embodiment, the filled polymer of thepresent invention is used as carpet backing. According to thisembodiment, a filler according to the invention comprising fly ash andhaving a particle size distribution having at least three modes iscombined with a polymer that is suitable for use as carpet backing,e.g., polyethylene, polypropylene, bitumen, styrene-butadiene copolymer,acrylonitrile-butadiene-styrene copolymer and blends thereof. A carpetmaterial in accordance with this embodiment can be produced by combiningthe polymer with the filler of the invention (and optionally othercomponents) to produce a filled polymer and applying the filled polymeras a melt to a surface of a carpet material at an elevated temperatureto form a backing on the carpet material. It may also be preferred toremove at least the fly ash particles having a particle size of greaterthan 250 microns prior to combining the filler with the polymer.Advantageously, it may also be useful to remove at least the fly ashparticles greater than, e.g., 150, 100, 75 or 50 microns, depending onthe application and the fly ash being used. The removal of coarseparticles can reduce equipment wear and tear and improve processability.For example, the fly ash particles can be passed through at least onescreen having a mesh size between about 75 and about 250 microns toremove at least the fly ash particles having a particle size of greaterthan 250 microns. In this embodiment, 40, 60, 80, 100 or 200 meshscreens are typically used. Alternatively, the fly ash particles can beair classified to remove at least the fly ash particles having aparticle size of greater than 250 microns. Typically, the filled polymeris formed into filled polymer pellets for ease of transportation,storage and handling. These pellets are subjected to an elevatedtemperature typically through extrusion to produce a filled polymer meltthat can be applied to the surface of the carpet material. The filler istypically included in the carpet backing at a filler loading of greaterthan 55% by weight, more preferably greater than 60% by weight.

The present invention will now be further demonstrated by the followingnon-limiting examples.

EXAMPLE 1 Methodology

The inventors have examined and compared fly ash fillers from a widerange of sources and with a wide range of compositions along withcommercially available calcium carbonates typically used as fillers bythe polymer composite industry. By way of example, the presentdisclosure provides information on the following materials: twocommercially available sources of calcium carbonate currently used inpolymer composites (CC01 and CC02); two fly ashes derived frombituminous coals (FA01 and FA02); three fly ashes derived from lignitecoals (FA03, FA04 and FA05); and two fly ashes derived fromsubbituminous coals (FA06 and FA07). An additional fly ash (FA08) wasincluded as an example of a processed fly ash. The chemicalcharacteristics and ASTM C-618 designations of the filler materialsexamined are given in Table 1.

TABLE 1 Sum ASTM C-618 Free Carbon Sample ID (SiO₂ + Al₂O₃ + Fe₂O₃)Designation (LOI, %) CC01 n/a carbonate CC02 n/a carbonate FA01 90.2Class F 2.1 FA02 91.5 Class F 1.9 FA03 81.9 Class F 0.2 FA04 86.5 ClassF 0.1 FA05 77.9 Class F 0.3 FA06 61.1 Class C 0.2 FA07 55.5 Class C 0.5FA08 82.0 Class F 0.2

Examination of the powders at high magnification by scanning electronmicroscopy (SEM) confirmed that, as is typical of such materials, allthe fly ash fillers examined were substantially spherical in particleshape. The two calcium carbonate samples were characteristically highlyirregular and blocky in particle shape. The fly ash fillers had asubstantially greater proportion of ultrafine particles, i.e., particleshaving a diameter of less than 5 microns, and had a higher surface areathan the calcium carbonate samples.

The granulometry of the fillers was examined by a variety of techniques.Specific gravity (true particle density) was determined using a heliumcomparison pycnometer (ASTM D-2840) and by the Le Chatelier method (ASTMC-188). The particle packing factor was determined by the oil absorptionmethod (ASTM D-281). The specific surface area was determined by theBlaine air permeability method (ASTM C-204). Analysis of the particlesize distribution of the fillers was conducted using a Horiba LA-300laser interferometer with isopropanol dispersion media. The fly asheswere obtained from power plants using pulverized coal and electrostaticor baghouse dust collection and typically had a multimodal form ofparticle size distribution. In particular, this was seen to take theform of a trimodal distribution with a coarse mode centered in theregion of 40-80 microns, an intermediate mode centered in the region of10-25 microns and an ultrafine mode typically centered in the region of0.3-1.0 microns. In some cases, a fourth coarse mode was observed in theregion of 100-200 microns. The multimodal distribution was convenientlyanalyzed into its component parts by mathematical deconvolution using acomputer program such as MATLAB® from Mathworks. The laser particle sizeanalyzer also calculated a specific surface area based on the observeddistribution. The differences between the fly ashes themselves and thecarbonate fillers are illustrated in Table 2 and demonstrate thedifferences between the specific gravity, the specific surface areas,the particle size parameters and the packing factors for the testedfillers.

TABLE 2 Specific Median Finer than Oil Packing Specific Surface Area*Particle Size 5 microns Absorption** Factor** Sample ID Gravity (cm²/g)(μm) (vol %) (g/100 g) (%) CC01 2.750 5,290 15.63 31.3 20.00 62.8 CC022.865 2,050 25.45 19.4 17.45 65.0 FA01 2.200 3,380 21.82 12.8 30.13 58.3FA02 2.290 3,160 25.22 12.8 30.13 57.4 FA03 2.270 5,400 12.86 28.6 18.7568.6 FA04 2.370 4,850 15.11 21.4 15.63 71.5 FA05 2.550 5,430 12.37 27.015.25 70.5 FA06 2.760 6,660 9.46 39.8 16.25 67.4 FA07 2.750 5,930 9.4140.5 20.00 62.8 FA08 2.516 7,690 2.64 80.2 25.13 59.5 *ASTM D-204 **ASTMD-281

As mentioned above, the molten polymer is typically processed at atemperature of 200-500° F. at which point the melt viscosity isdesirably 300-5000 centipoise or more and after adding the appropriatequantity of filler, the filled polymer thickens considerably with aresulting plastic viscosity of 3000-10,000 or more being typical in theindustry. To compare the fillers tested in the present examples, alaboratory model was established to simulate the process conditions. Forconvenience and precision, rheological runs were conducted at ambienttemperature using a asphalt/linseed oil fluid system as a surrogate formolten asphalt that was adjusted to provide an unfilled baselineviscosity of 400 cps at 400-425° F. Additional analysis confirmed thatthe surrogate system was entirely comparable with properties of moltenasphalt at a typical process temperature of 400-425° F., without theexperimental problems and errors associated with handling hot asphalt.The surrogate is also analogous to polymer systems generally at theirnormal processing temperatures.

The rheological properties of the filled polymer fluid composites weredetermined using a computer controlled MC-III rheometer as described inU.S. Pat. Nos. 5,321,974 and 5,357,785. All test mixtures were examinedafter mixing to full dispersion before recording the stress/strain flowcurves on the rheometer. Most of the fluid composites exhibited typicalBingham plastic flow at lower filler loadings, enabling the readydetermination of Bingham plastic viscosity and yield stress parameters.At the higher filler loadings, many of the composites exhibitedcharacteristic pseudoplastic flow, at which point the systems had anoticeably thicker consistency. For each filler system examined, flowcurves were recorded as a function of filler loading, from whichcomputation enabled the determination of the filler loading, expressedby weight (as Cw %) and by volume (as Cv %) required to produce alimiting composite viscosity of 6000 cps. Additional computationsdetermined the plastic viscosity for each filled system at specificdesign targets, examples being 70% by weight loading (Cw=70%), 65% byweight loading (Cw=65%) and 45% by volume loading (Cv=45%). Therelationships between filler loading and viscosity are provided in Table3.

TABLE 3 Sample Cw % Cv % cps at cps at cps at ID for 6000 cps for 6000cps Cw = 70% Cw = 65% Cv = 45% CC01 71.6 47.7 3,303 2,072 3,800 CC0268.9 44.9 4,689 3,469 6,100 FA01 63.9 43.7 19,743 6,640 8,300 FA02 63.441.5 17,649 7,771 10,800 FA03 72.6 54.2 2,559 1,432 1,600 FA04 75.0 55.32,275 1,578 1,800 FA05 74.1 53.2 3,378 2,447 3,100 FA06 74.3 49.6 3,9703,030 4,800 FA07 72.2 46.5 3,970 2,522 4,600 FA08 63.8 39.8 10,162 6,6287,800

From the forgoing, it is evident that the different filled polymercomposite systems can exhibit substantially different rheologicalproperties as a function of both mineral filler type and filler loading.This is true not only for the fly ash fillers themselves, but also incomparing the fly ash fillers with the calcium carbonate fillers. It isimmediately obvious that two of the fly ashes, FA01 and FA02, can beonly be loaded to about 63-64% by weight of polymer to reach the targetcomposite viscosity of 6000 cps. Allowing for differences in specificgravity, this translates into a volume loading of 41.5-43.7%, somewhatless than that for the two carbonate fillers, which achieved volumeloadings of 44.9-47.7%. In comparison, fly ashes FA03-FA07 can be loadedinto the polymer to a much higher degree, up to 75% by weight, beforethe target of 6000 cps is reached. Again, allowing for the differencesin specific gravity between the materials, this translates into a volumeloading that reached 55.3% in the case of FA04. This demonstrates thatan optimally selected fly ash filler can be used at substantially higherloadings than the calcium carbonate fillers before excessive thickeningoccurs. Inspection of the data in Table 3 also shows that optimallyselected fly ash fillers, such as FA03, FA04 and FA05, allowsubstantially higher loadings, up to 10% by volume, compared to thecalcium carbonate fillers, CC02 and CC02. Higher filler loadingstranslate into significant cost savings, most obviously in terms ofsavings in raw polymer used and energy consumption.

As mentioned above, the fillers tested in this example typicallypossessed a trimodal particle size distribution with a coarse modecentered in the region of 40-80 microns, an intermediate mode centeredin the region of 10-25 microns and an ultrafine mode typically centeredin the region of 0.3-1.0 microns. The inventors have determined that therelationship between the volume percentages of the particles in each ofthe modes and particularly the mode ratio based on the volume ofparticles in modes 2 and 3 to the volume of particles in mode 1 providesa value that demonstrates the advantage of certain fillers. Inparticular, mode ratios in the range of 4.5-7.5 have been found to beparticularly advantageous. The mode ratios for the fillers tested areprovided in Table 4.

TABLE 4 Mode 1 Mode 2 Mode 3 (M1) (M2) (M3) Mode Ratio Sample ID vol %vol % vol % (M2 + M3)/M1 CC01 23.2 46.9 29.9 3.3 CC02 14.1 12.4 73.5 6.1FA01 8.9 65.9 25.2 10.2 FA02 26.6 67.6 24.5 11.7 FA03 16.2 71.0 12.9 5.2FA04 11.7 67.4 20.9 7.5 FA05 13.6 73.3 13.1 6.4 FA06 29.7 57.4 13.0 2.4FA07 28.7 61.5 9.9 2.5 FA08 16.5 83.5 0.0 5.1

It is noted that the FA06 and FA07 samples have low (M2+M3)/M1 ratiosdue to an excess of ultrafine particles, i.e., a lack of coarseparticles. FA01 and FA02 have high ratios due to lack of fine particles,i.e., an excess of coarse particles. The FA03, FA04 and FA05 sampleswere found to have particularly advantageous volume loadings andincluded particle size distributions that included 11-17% of theparticles by volume in the first mode, 67-74% of the particles by volumein the second mode, and 12-21% of the particles by volume in the thirdmode, to produce the desired modal ratio.

As discussed herein, the inventors have determined that the differencesbetween the fillers are substantially ascribable to the granulometry ofthe fillers. One parameter that is particularly useful in this regard isthe particle packing factor that shows a strong relationship to thedetermined plastic viscosity as is shown in Table 5.

TABLE 5 Packing Factor (%) Viscosity (cps) Sample ID ASTM D-281 at Cw =70% CC01 62.8 3,303 CC02 65.0 4,689 FA01 58.3 19,743 FA02 57.4 17,649FA03 68.6 2,559 FA04 71.5 2,275 FA05 70.5 3,378 FA06 67.4 3,970 FA0762.8 3,970 FA08 59.5 10,162

In this way, and in concert with the rheological data, it possible tocompute the particle packing factor that will provide the lowest plasticviscosity at a specific filler loading design goal. The resultinglimiting packing factors for various filler design loadings in thesurrogate are collected in Table 6.

TABLE 6 Filler Loading Design Limiting Packing Factor Cw = 65% 61.1 Cw =70% 64.1 Cv = 45% 62.3

Similar relationships can be established with the other granulometryparameters such as the particle size distribution and in particular, themodality of the particle size distribution.

The data provided in Table 5 demonstrates that two of the “Class F”fillers, FA01 and FA02, have very high composite plastic viscosity atthe nominal loading of Cw=70%. At the same time, these two fillers havethe lowest packing factors in the group. The processed fly ash, FA08,also a “Class F” fly ash according to the ASTM definition, similarly hasa low packing factor and a high composite plastic viscosity. The other“Class F” fillers, FA03, FA04 and FA05, all have high packing factorsand correspondingly low composite plastic viscosities. Furthermore, theinventors have shown clearly that the two ASTM “Class C” fly ashes, FA06and FA07, can function perfectly well as fillers, as evidenced by theirpacking factor and plastic viscosity.

Furthermore, these fillers can improve the mechanical properties of thepolymer composite when compared to polymer composites using conventionalfillers. For example, as discussed in related U.S. application Ser. No.09/993,316, filed Nov. 14, 2001, the fly ash fillers of the inventioncan be used at higher loadings to produce greater tear strength andtensile strength in asphalt shingles, which are one type of polymercomposite in accordance with the invention.

EXAMPLE 2 Modification of Granulometry of Fly Ash to Improve FillerCharacteristics

As a further illustration of the broader application of the conceptsdisclosed in the present invention, the inventors have demonstrated thatit is possible to modify the granulometry of a fly ash throughprocessing and/or blending in such a way that its characteristics as amineral filler are markedly enhanced.

As an example, it will be recalled from Example 1 that fly ash FA01,designated as an ASTM “Class F” ash, does not function satisfactorily asa polymer filler as a result of a sub-optimal granulometry, whereby theparticle packing factor is low (58.3%) and the composite plasticviscosity is very high (12,123 cps) at a loading of 70% by weight.Further examination by scanning electron microscopy revealed that flyash FA01 has a relatively low population of ultrafine particles leadingto a low specific surface area of 3,380 cm²/g. A series of experimentswas carried out where additional fine particulate material was added toFA01 using the fine processed ash FA08 with a specific surface area of7,690 cm²/g. At each addition level, the granulometry of the resultingfiller blend was measured and the rheological characteristics determinedusing the MC-III rheometer at a nominal fixed filler content of 70% byweight. Granulometry and rheological data for the blended fillersproduced with various proportions of fly ashes FA01 and FA08 aresummarized in Table 7.

TABLE 7 Specific Surface Packing Factor Viscosity (cps) Sample (cm²/g)(%) at Cw = 70% 100% FA01 3380 58.3 12,123 90:10 FA01/FA08 3374 59.98,765 80:20 FA01/FA08 3759 60.8 6,651 70:30 FA01/FA08 4125 68.2 5,59060:40 FA01/FA08 4409 67.9 5,353

From inspection of the results in Table 7, it is evident that as theproportion of the fine particulate fly ash FA08 increases from 0-40% byweight in the blend, both the specific surface area and the particlepacking factor increase monotonically. This is accompanied by acorresponding marked, and substantially linear, decrease in thecomposite plastic viscosity from over 12,000 cps to a pessimum value of5,353 cps at a 40% by weight content of fly ash FA08. This illustratesthe synergistic benefits of the blending or modifying of fly ashes inaccordance with the present invention, especially when it is consideredthat the composite plastic viscosity of the fine fly ash FA08 by itselfis 10,162 cps at a filler content of 70% by weight. It is convenient toconsider that, initially, the addition of fine particles in fly ash FA08compensates for the deficiency of fine particles in fly ash FA01,thereby improving the packing. This proceeds up to a certain additionlevel, or pessimum, at which point the system develops an excess of fineparticles or deficiency of coarse particles, with a consequent reductionin the packing efficiency.

As a second example, alternative modification of the granulometry of flyash FA01 was carried using progressively increasing proportions of flyash FA06, an ASTM “Class C” ash with an inherently higher content offine particles, as shown by its specific surface area of 4,026 cm²/g. Asclearly shown by the data in Table 8, there was again a progressive, andsubstantially linear, increase in both the specific surface area andparticle packing factor of the blended filler up to approximately 60% byweight of fly ash FA06. This was again accompanied by a marked reductionin the composite plastic viscosity from an initial value of 7,766 cpsfor the 100% FA01 down to a pessimum value of 2,206 cps for a 40:60 byweight blend of fly ashes FA01 and FA06. As in the previous example, theaddition of the fine “Class C” fly ash FA06 increased the proportion offine particles in the fly ash FA01 up to a point, occurring around 60%by weight of fly ash FA06, a point above which the system began to bedeficient in coarse particles, with a consequent reduction in packingefficiency.

TABLE 8 Specific Surface Packing Factor Viscosity (cps) Sample (cm²/g)(%) at Cw = 70% 100% FA01 2,929 61.6 7,766 80:20 FA01/FA06 2,862 63.05,315 60:40 FA01/FA06 3,176 65.9 3,780 40:60 FA01/FA06 3,487 68.0 2,20620:80 FA01/FA06 4,026 69.5 4,931

These modifications to the granulometry of a fly ash provide a number ofsignificant advantages to its successful use as a mineral filler inpolymer composites, including: (i) increased mineral filler loadings ata given composite viscosity, resulting in cost savings through reducedpolymer consumption and reduced energy requirements; (ii) potentiallyunusable or uneconomic fly ash fillers could be made viable, therebyimproving economics and reducing the environmental impact of fly ashthat would otherwise require disposal; (iii) reduced viscosity at agiven mineral filler loading, with the benefit that energy savings wouldaccrue through lower energy consumption to heat the polymer; (iv) anexpected improvement in certain mechanical properties; and (v) improvedmanufacturing economics.

EXAMPLE 3 Modifying the Granulometry of Calcium Carbonate with Fly Ashto Improve Filler Characteristics

As discussed herein, ground limestone or calcium carbonate is themineral filler conventionally used in many polymer composites. Becauseof the irregular particle size and poor particle packing properties ofcalcium carbonate fillers, the amount of commercially available calciumcarbonate fillers that can be loaded in polymer composites is typicallylimited.

In another illustration of the broader application of the technology,the inventors have shown that it is possible to markedly improve thefiller characteristics of commercial calcium carbonates by modifyingtheir granulometry by blending the calcium carbonate fillers withcertain selected fly ashes.

By way of example, the inventors have selected a typical commercialcalcium carbonate, CC02, currently used in polymer shingle manufactureand having a low specific surface area and a deficiency of fineparticles. As discussed earlier, rheological examination of thiscarbonate showed that it would reach a composite plastic viscosity of6,000 cps at a loading of 68.9% by weight, corresponding to 44.9% byvolume. Modification of the granulometry of carbonate CC02 was carriedout by blending in progressive increments of fly ash FA06, an ASTM“Class C” ash. Inspection of the data in Table 9 shows that withincreasing amounts of the blend ash FA06, there was a marked beneficialincrease in the packing factor from 65% to over 70%. At the same time,the plastic composite viscosity decreased from 4,647 cps for the 100%CC02 material down to 3,112 cps for a 50:50 by weight blend of carbonateCC02 with fly ash FA06. With this kind of improvement in fillerefficiency in the modified blend, the filler loading can be readilyincreased to 70-73% by weight, or more, before a composite viscosity of6,000 cps is reached.

TABLE 9 Specific Surface Packing Factor Viscosity (cps) Sample (cm²/g)(%) at Cw = 70% 100% CC02 2050 65.0 4,647 80:20 CC02/FA06 2063 69.93,895 60:40 CC02/FA06 2872 70.2 3,492 50:50 CC02/FA06 3,112 100% FA066660 67.4 4,775

Calcium carbonate/fly ash blends can contain up to 50 wt % or more flyash, ideally selected from ashes that possess a substantially greaterproportion of ultrafine particles compared with the original calciumcarbonate. These can include ASTM “Class F” and “Class C” fly ashesderived from the combustion of bituminous, lignite and subbituminouscoals, and in more specific ideal cases from lignite and subbituminouscoals. Alternatively, a coarse calcium carbonate can serve to increasethe coarse particle content of a fly ash filler that is deficient incoarse particles. It is believed that filled polymer composites madewith calcium carbonate/fly ash blends will often have improved physicalproperties as evidenced in pending U.S. patent application Ser. No.09/993,316 by the increases in tear and tensile strength when thesefillers are used in asphalt shingles.

As mentioned above, the mode ratio for the fillers has been found to bea particularly useful parameter in determining whether the fillers willhave the desired packing factor and will provide good filler propertiesin the polymer composite. The mode ratios for the preferred fillerblends discussed in Examples 2 and 3 are provided in Table 10 and fallwithin the desired range of 4.5 to 7.5.

TABLE 10 Mode 1 Mode 2 Mode 3 (M1) (M2) (M3) Mode Ratio Sample ID vol %vol % vol % (M2 + M3/M1) 60:40 FA01/FA08 15.8 66.2 18.0 5.3 40:60FA01/FA06 16.4 61.7 22.0 5.1 60:40 CC02/FA06 17.7 37.7 44.6 4.7

As shown in the above examples, the fly ash fillers and filler blendsused in accordance with the invention allow high filler loadings at theviscosities and temperatures conventionally used to make polymercomposites and can provide improved mechanical properties compared tocommercially available fillers (e.g. calcium carbonate). The inventorshave found that a filler having a particle size distribution with atleast three modes exhibits improved rheology and can be used at higherloadings in polymer composites and can often result in improvedmechanical properties. Specifically, a particle size distribution withthree modes is believed by the inventors to give optimum packing densityand to produce a polymer composite having the improved mechanicalproperties mentioned above.

It is understood that upon reading the above description of the presentinvention, one skilled in the art could make changes and variationstherefrom. These changes and variations are included in the spirit andscope of the following appended claims.

1. A filler for a filled polymer comprising a blend of at least twodissimilar types of fly ash, each selected from the group consisting ofsubbituminous coal fly ash, lignite coal fly ash, Class C fly ash, ClassF fly ash, and combinations thereof, said filler blend having a packingfactor of at least 65% and a particle size distribution having at leastthree modes, a first mode having a first median particle diameter, asecond mode having a second median particle diameter that is greaterthan the first median particle diameter, and a third mode having a thirdmedian particle diameter that is greater than the second median particlediameter, wherein the volume of particles in the second mode is greaterthan the volume of particles in the third mode.
 2. The filler accordingto claim 1, wherein the median particle diameter is from 0.3 to 1.0microns, the second median particle diameter is from 10 to 25 microns,and the third median particle diameter is from 40 to 80 microns.
 3. Afiller for a filled polymer comprising a blend of at least twodissimilar types of fly ash, each selected from the group consisting ofsubbituminous coal fly ash, lignite coal fly ash, Class C fly ash, ClassF fly ash, and combinations thereof, said filler blend having a packingfactor of at least 65% and a particle size distribution having at leastthree modes, wherein the filler blend includes a first mode having amedian particle diameter from 0.3 to 1.0 microns, a second mode having amedian particle diameter from 10 to 25 microns, and a third mode havinga median particle diameter form 40 to 80 microns, wherein the particlesize distribution of the filler blend includes 11-17% of the particlesby volume in the first mode, 56-74% of the particles by volume in thesecond mode, and 12-31% of the particles by volume in the third mode. 4.The filler according to claim 2, wherein the ratio of the volume ofparticles in the second and third modes to the volume of particles inthe first mode is from about 4.5 to about 7.5.
 5. The filler accordingto claim 1, wherein the filler blend comprises a first fly ash fillerhaving a median particle size of 10 microns or less and a second fly ashfiller having a median particle size of 20 microns or greater.
 6. Thefiller according to claim 1, wherein the filler blend comprises a blendof a subbituminous coal fly ash filler and a lignite coal fly ashfiller.
 7. The filler according to claim 1, wherein the filler blendcomprises a blend of a Class C fly ash and a Class F fly ash.
 8. Afiller for a filled polymer comprising a blend of a first fly ash fillerand at least one additional filler wherein the filler blend has apacking factor of at least 65% and a particle size distribution havingat least three modes, wherein a first mode has a first median particlediameter, a second mode has a second median particle diameter greaterthan said first median particle diameter, a third mode has a thirdmedian particle diameter greater than said second median particlediameter, and the volume of particles in the second mode is greater thanthe volume of particles in the third mode.
 9. The filler according toclaim 8, wherein the particle size distribution of the filler includes afirst mode having a median particle diameter from 0.3 to 1.0 microns, asecond mode having a median particle diameter from 10 to 25 microns, anda third mode having a median particle diameter from 40 to 80 microns.10. The filler according to claim 9, wherein the particle sizedistribution of the filler blend includes 11-17% of the particles byvolume in the first mode, 56-74% of the particles by volume in thesecond mode, and 12-31% of the particles by volume in the third mode.11. The filler according to claim 9, wherein the ratio of the volume ofparticles in the second and third modes to the volume of particles inthe first mode is from about 4.5 to about 7.5.
 12. The filler accordingto claim 8, wherein the at least one additional filler in the fillerblend is a second fly ash.
 13. The filler according to claim 12, whereinthe filler blend comprises a first fly ash filler having a medianparticle size of 10 microns or less and a second fly ash filler having amedian particle size of 20 microns or greater.
 14. The filler accordingto claim 8, wherein the at least one additional filler in the fillerblend is calcium carbonate.
 15. The filler according to claim 8, whereinthe filler blend comprises a subbituminous coal fly ash filler.
 16. Thefiller according to claim 8, wherein the filler blend comprises alignite coal fly ash filler.
 17. The filler according to claim 8,wherein the filler blend comprises a Class C fly ash.
 18. The filleraccording to claim 8, wherein the filler blend comprises a Class F flyash.
 19. A fly ash filler for use in a polymer composite having apacking factor of at least 65% and a particle size distribution with atleast three modes, wherein a first mode has a first median particlediameter, a second mode has a second median particle diameter greaterthan said first median particle diameter, a third mode has a thirdmedian particle diameter greater than said second median particlediameter, and the volume of particles in the second mode is greater thanthe volume of particles in the third mode.
 20. The filler according toclaim 19, wherein the particle size distribution of the filler includesa first mode having a median particle diameter from 0.3 to 1.0 microns,a second mode having a median particle diameter from 10 to 25 microns,and a third mode having a median particle diameter from 40 to 80microns.
 21. The filler according to claim 20, wherein the particle sizedistribution of the filler includes 11-17% of the particles by volume inthe first mode, 56-74% of the particles by volume in the second mode,and 12-31% of the particles by volume in the third mode.
 22. The filleraccording to claim 20, wherein the ratio of the volume of particles inthe second and third modes to the volume of particles in the first modeis from about 4.5 to about 7.5.
 23. The filler according to claim 19,wherein the fly ash comprises a subbituminous coal fly ash filler. 24.The filler according to claim 19, wherein the fly ash comprises alignite coal fly ash filler.
 25. The filler according to claim 19,wherein the fly ash comprises a Class C fly ash.
 26. The filleraccording to claim 19, wherein the fly ash comprises a Class F fly ash.27. A filler for a filled polymer comprising a blend of a first fly ashfiller and at least one additional filler wherein the filler blend has apacking factor of at least 65% and a particle size distribution havingat least three modes, wherein a first mode has a median particlediameter from 0.3 to 1.0 microns, a second mode has a median particlediameter from 10 to 25 microns, and a third mode has a median particlediameter from 40 to 80 microns, and wherein the particle sizedistribution of the filler blend includes 11-17% of the particles byvolume in the first mode, 56-74% of the particles by volume in thesecond mode, and 12-31% of the particles by volume in the third mode.28. A fly ash filler for use in a polymer composite having a packingfactor of at least 65% and a particle size distribution with at leastthree modes, wherein a first mode has a median particle diameter from0.3 to 1.0 microns, a second mode has a median particle diameter from 10to 25 microns, and a third mode has a median particle diameter from 40to 80 microns, and wherein the particle size distribution of the fillerincludes 11-17% of the particles by volume in the first mode, 56-74% ofthe particles by volume in the second mode, and 12-31% of the particlesby volume in the third mode.